The standardization of Access Gateways (AGw) has been ongoing in the Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) organization for some time. Initially, the standardization focused on an H.248 link to Soft Switches, and later addressed connecting AGw's to an IP Multimedia Subsystem (IMS) network by adding an Access Gateway Control Function (AGCF) that converts between SIP and H.248. The purpose of the AGCF is to enable the reuse of existing AGw's to connect users to the IMS.
FIG. 1 is a simplified block diagram illustrating an existing network architecture 10 for controlling an Access Gateway (AGw) 11 from a Soft Switch 12. The Access Gateway provides call handling for users 13 in the Public Switched Telephone Network (PSTN) who are accessing an Internet Protocol (IP) backbone network 14. The Access Gateway may act as a proxy toward the IP backbone network. The Access Gateway is controlled through the IP backbone network from the Soft Switch utilizing an H.248 control link 16. Access Gateway Management Systems 17 may connect to the Access Gateway through a Simple Network Management Protocol (SNMP) link 18 and the IP backbone network.
If the H.248 control link fails, the Access Gateway 11 can still route emergency calls from the PSTN to a pre-connected/configured port for the emergency numbers. The Access Gateway can also set up PSTN calls to other PSTN users connected to the same gateway. However, when all call setups are controlled by the H.248 control link, a link between groups of access gateway systems to connect a larger group of subscribers is not supported when the H.248 control link fails.
When setting up calls, the Access Gateway 11 does not have knowledge of the dialing or directory numbers. The connectivity of subscribes is controlled from the Soft Switch 12 with a termination identity used in the H.248 commands that has been provisioned in the Soft Switch, with a relation to the directory number. The Soft Switch knows only that the user is connected to an access gateway with its termination ID and what H.248 control link (e.g., UDP address) the user can be reached on.
Thus, in the event of an H.248 control link failure, the existing architecture does not function to enable call setup in an open environment over standardized interfaces.